XSS in Mybb
CVE-2020-15139
In MyBB before version 1.8.24, the custom MyCode (BBCode) for the visual editor doesn't escape input properly when rendering HTML, resulting in a DOM-based XSS vulnerability. The weakness can be exploited by pointing a victim to a page where the visual editor is active (e.g. as a post or Private Message) and operates on a maliciously crafted MyCode message. This may occur on pages where message content is pre-filled using a GET/POST parameter, or on reply pages where a previously saved malicious message is quoted. After upgrading MyBB to 1.8.24, make sure to update the version attribute in the `codebuttons` template for non-default themes to serve the latest version of the patched `jscripts/bbcodes_sceditor.js` file.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.013 (69.7th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 70th percentile — 69.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.013 · newest: 0.013 · change: 0.000
Affected products
- Mybb — versions < 1.8.24
Weakness classification (CWE)
Public proof-of-concept exploits
References
- github.com/mybb/mybb/security/advisories/GHSA-37h7-vfv6-f8rj (Patch, Third Party Advisory)
- github.com/mybb/mybb/commit/37ad29dcd25489a37bdd89ebac761f22492558b0 (Patch, Third Party Advisory)
- mybb.com/versions/1.8.24/ (Patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2020-15139?
- CVE-2020-15139 is a high-severity vulnerability in Mybb, classified under Cross-site Scripting. CVSS score: 8.8/10. Published 2020-08-10.
- How severe is CVE-2020-15139?
- High severity. CVSS v3 base score is 8.8 out of 10.
- Is CVE-2020-15139 known to be exploited?
- 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.